It is necessary in many systems to bring a movable member to a stop at a precise location. For example, in a magnetic memory disk device bearing a number of information and servo tracks, it is required that the read/write head be positiond over a particular track. Likewise, in a high speed printer with intermittent print wheel movement, it is required that the print wheel be rotated so that a particular character is in the print position.
A position measuring transformer known as an Inductosyn is often used for achieving such positioning. The Inductosyn device, whether in a linear or rotary form, senses the movement of a shaft member based on the inductive coupling between a winding or windings on a fixed insulating member and a winding or windings on a movable insulating member separated from the fixed member by a small air gap. In a rotary transformer the members would be disks and each winging would incliude a multiplicity of radially extending strip-like conductors connected in series by circumferential conductors so that alternate conductors carry current in the same direction and adjacent conductors carry current in radially opposite directions. The conductors are identical in shape and are spaced at uniform angular intervals in a circular arcuate array about the center of a pattern which they establish, the center being the effective center of the disk.
To achieve the high degree of accuracy needed for satisfactory operation, the conductors are deposited on the disk by a photoetching process. Generally, that process can provide a minimum conductor spacing sufficient to allow for only 32 tracking positions for each 21.degree. of a two inch diameter disk. However, with the increasing track density now possible with magnetic disks, it is desired that greater than 32 tracking positions be available for each 21.degree. of disk rotation. Accordingly, there is a need for a transducer system that can accommodate an increased number of tracking positions.